Device and method for estimating the attention level of a driver of a vehicle

ABSTRACT

The invention pertains to a method for estimating the attention level of the driver of a vehicle in a traffic lane, comprising the following steps: —the continuous capture of images (10) of the ground, —the reconstruction of an serial view (11, 12) of a ground segment at successive instants t, —the reconstruction of an serial view (11, 12) of a road segment at successive current instants t, —the estimation of the lateral position of the vehicle (100) in the reconstructed serial view (11, 12), and the storage of said estimated positions of the vehicle, —the determination of an estimated attention level of the driver at a past instant t3, as a function: ∘of the evolution of the lateral position of the vehicle, ∘of the analysis of the profile of a road portion at least partially situated upstream of the vehicle at the instant t3.

The invention pertains to the field of devices designed for assisting the driving of vehicles, in particular to the methods for assessing the driver's attention.

The invention relates more specifically to a method for assessing the ability of the driver of a vehicle to keep the vehicle in its traffic lane, in order to assess his level of attention and, if necessary, to warn him when he potentially unwillingly crosses a delimitation line of a traffic lane.

Today, motor vehicles include many driver assistance systems. These systems are referred to by the acronym well known to those skilled in the art of ADAS, or Advanced Driver Assistance Systems.

Such driver assistance systems equip more and more motor vehicles. Most of the functions provided by these ADAS systems require the vehicle to be able to detect the lane in which it is located.

Among these functions, the association of transmission data from a frontal camera, capturing images of the road, in front of the vehicle, and data from a camera located in the passenger compartment, filming the face of the vehicle driver, can be used to determine a level of attention or inattentiveness of the driver.

Indeed, at present, the development of technologies relating to autonomous vehicles, and more recently, to driving assistance functions involving vehicle automation phases, is such that the information relating to the level of attention or inattentiveness of the driver is crucial, especially for the purpose of a possibly necessary resumption of the control of the vehicle.

In this context, the images from the frontal camera are analyzed so as to estimate the lateral position of the vehicle in its traffic lane, in particular to detect a possible unwanted crossing of the line.

In the state of the art, the information relating to the lateral position of the vehicle in its traffic lane is generally available only via the frontal camera and therefore strongly depends on the intensity and availability of the images that it captures.

Some vehicles are indeed equipped with such a frontal camera capable of determining the lateral position of the vehicle in a traffic lane. However, as is known, the data from such a frontal camera can be altered because of the hypothesis used, and generally erroneous, of “level ground”, or because of the hypothesis used, and generally erroneous, of the horizontal attitude of the vehicle, etc.

In addition, for all these systems, calibration parameters of the cameras to calculate the relative position of the lines relative to the vehicle [incomplete sentence]. This makes them sensitive to any de-calibration (shock on a camera, change of attitude of the vehicle according to its load, etc.). Likewise, these systems consider that the ground is a horizontal plane in the vehicle marker. This hypothesis is not always verified and this leads to positioning errors when the road goes up or down, or when the road has a deviation on the ground portion used to detect the line.

Thus, in practice, according to the state of the art, the lateral position of a vehicle in a traffic lane is an information exploited by several driving assistance functions and for the assessment of the level of attention of the driver, including in combination with an image analysis of the driver's face.

The system thus observes in particular the evolution of the lateral position of the vehicle over time to estimate a crossing of the line and alert the driver.

The document FR2947769_A 1 describes a system comprising a camera located at the rear of the vehicle, designed to allow the tracking of the vehicle trajectory for the purpose of sending an alert to the driver in case of deviation from a predetermined ideal trajectory. This document is representative of the state of the art.

Today, the information relating to the position of the vehicle in a traffic lane is generally determined in real time from the images captured by a frontal camera.

However, in addition to the defects related to imprecision, or even the impossibility estimating the lateral position of the vehicles in their traffic lanes, another defect of these systems is that the calibration parameters of the cameras used must be finely regulated. This makes them sensitive to any “de-calibration” caused by a shock on a camera, a change of attitude of the vehicle, etc. Similarly, these systems consider that the ground is a horizontal plane in the vehicle marker, which constitutes an overall erroneous hypothesis.

Moreover, in order to assess the level of attention of the driver and to effectively detect a possible untimely crossing of the line, it is useful to store, by road segment, the evolution over time of the relative lateral position of the vehicle in its traffic lane.

Thus, in order to effectively solve the problem raised above, without creating new drawbacks, it is envisaged to integrate images of the ground captured by at least one camera for a certain period of time, so as to eliminate errors due to inconsistencies or to local unavailability. Thanks to the captured images, the method according to the invention allows the creation of an aerial view of the vehicle in its traffic lane, integrated over a certain period of time.

Moreover, by following and anticipating the evolution over time of the lateral position of the vehicle in its lane, and preferably by associating this tracking with an adapted analysis of captured images of the drivers face, the method according to the invention allows to assess the level of attention of the driver.

For this purpose, the method for assessing the level of attention of the driver of a vehicle, taking into account the evolution of the lateral position of the vehicle in a traffic lane, according to the invention, comprises reconstituting an aerial view of a road segment obtained by storing, as and when the vehicle moves, a portion of the ground located closest to the vehicle. Furthermore, the method according to the invention comprises the positioning of the vehicle, at a previous instant, in said reconstituted aerial view, as well as the storing of the successive positions of the vehicle, on the given road segment. The present invention thus allows the creation of an aerial view of a portion of road located in the time marker of the vehicle, upstream of said vehicle.

According to an advanced embodiment of the method according to the invention, the combination of an image analysis of the drivers face to the analysis of the successive positions of the vehicle in the aerial view allows to precisely determine a level of attention of the driver of the vehicle.

More specifically, the invention relates to a method for assessing the attention level of the driver of a moving vehicle in a traffic lane, comprising the following steps:

-   -   capturing images of the ground continuously, at the front and/or         at the rear of the vehicle, by means of at least one adapted         camera, said images corresponding to a ground surface having a         width at least equal to one width and a depth of a traffic lane,     -   reconstructing an aerial view of a road segment at successive         current instants t, by integrating over time the images captured         between an instant t1=t−dt1 and the current instant t, dt1 being         positive,     -   estimating the lateral position of the vehicle in the aerial         view reconstructed at said successive current instants t, and         storing said estimated positions of the vehicle between an         instant t2=t−dt2 and the current instant t, dt2 being positive         and independent of dt1     -   determining an estimated level of attention of the driver at an         instant t3=t−dt3, dt3 being positive, the instant t3 being         posterior to the instant t2 and the instant t3 being posterior         or equal to the instant t1, according to:         -   the evolution of the lateral position of the vehicle in the             aerial view between the instants t2 and t3,         -   the analysis of the profile of a portion of a road belonging             to the reconstructed aerial view at the current instant t             and corresponding to a sequence of images captured between             the instant t1 and the current instant t, said portion of a             road being at least partially located upstream of the             vehicle at the instant t3.

Thus, thanks to the method according to the invention, it is possible to have an aerial view giving, in the time marker of the vehicle, a portion of the road section located upstream of the vehicle at instant t3. The analysis of the evolution of the lateral position of the vehicle over time is used to assess the level of attention of the driver.

According to one embodiment, after the step of reconstructing an aerial view of the ground, the detection of at least one line forming a ground marker delimiting a traffic lane in said reconstructed aerial view, the estimation of the position of the vehicle in the reconstructed aerial view consisting of determining the relative position of said vehicle with respect to said at least one line.

According to a preferred embodiment, the method furthermore comprises:

-   -   capturing images of the driver's face,     -   analyzing the images of the driver's face, determining the         driver's level of attention being also a function of said         analysis of the images of the driver's face.

According to one embodiment, the estimation of the relative position of the vehicle with respect to said at least one line in the reconstructed aerial view comprises the assembly of successive captured images corresponding to a ground surface having a depth determined as a function of the speed of the vehicle.

According to one embodiment, the detection of at least one line forming a ground marker delimiting a traffic lane in the reconstructed aerial view comprises the implementation of a Hough transform.

According to one embodiment, the method according to the invention further comprises a warning step of the driver when the vehicle crosses said at least one line.

Advantageously, said lane width may be equal to five meters.

Advantageously, said depth of the ground surface of the images captured is less than two meters.

The present invention also relates to a device for estimating the lateral position of a vehicle in a traffic lane, comprising at least one camera for performing the capture of images of the ground continuously, at the front and/or at the rear of the vehicle, a calculation unit and a storage unit, configured to implement the method according to one of the preceding claims.

Advantageously, said at least one camera is a frontal camera disposed at the front of the vehicle.

Other features and advantages of the invention will appear on reading the detailed description of the embodiments of the invention, given by way of example only, and with reference to the drawings which show:

FIG. 1, the block diagram of the steps of the method for assessing the level of attention of the driver of a vehicle, according to the invention,

FIG. 2, the diagram graphically representing the process of estimating the lateral position of the vehicle, according to a preferred embodiment of the method according to the invention.

In what follows, the embodiments described are more particularly related to an implementation of the device according to the invention within a motor vehicle. However, any implementation in a different context, particularly in any type of land vehicle, is also covered by the present invention.

FIG. 1 represents functional blocks materializing the steps of the method according to the invention.

Thus, the method according to the invention provides a first step 1 of image capture of the ground at the front and/or rear of the vehicle, continuously. The captured images correspond to a ground surface having a width corresponding at least to a width of a traffic lane, i.e. about 5 meters. The camera used can thus be a frontal camera capturing images of the ground at the front of the vehicle, or a camera placed at the rear, such as a parking aid camera, whose successive captured images are integrated over time to form successive reconstructed aerial views.

Indeed, from the captured images, the method according to the invention comprises a step 2 of reconstruction of aerial views at successive current instants t of a road segment, by integrating over time the images captured between an instant t1=t−dt1 and the current instant t, dt1 being positive.

It should be noted that, said aerial view not being intended to be displayed, a fine alignment is not required. According to one embodiment, a registration of the images is nonetheless provided for according to the estimated movement of the vehicle by means of odometric data obtained using suitable sensors measuring wheel tops or the steering wheel angle for example.

According to one embodiment, an overlapping of the images captured successively is provided, in particular to facilitate the detection of lines of separation of traffic lanes and improve the connections between successive images.

From the reconstructed aerial view, the method according to the invention provides a step 3 for estimating the lateral position of the vehicle on the road segment, in its traffic lane. The successive lateral positions of the vehicle on the road segment are calculated at each current instant t. In addition, said estimated positions of the vehicle are stored between an instant t2=t−dt2 and the current instant t, dt2 being positive and independent of dt1.

To this end, according to a preferred embodiment, the method comprises the detection of one or more ground marking lines materializing the delimitation between the traffic lanes.

There are thus known techniques for detecting lines in an image. For example, the detection of lines in the reconstructed aerial view can be realized by the implementation of a Hough transform. The Hough transform allows to identify all the lines passing through a point (Y, X) of the ground. Conversely, for a pair of coefficients (a, b) defining a straight line, the Hough transform allows to identify the set of points (X, Y) located on this line. The coefficients ‘a’ and ‘b’ correspond respectively to the angle formed by the line with the Y-axis, and to the distance from the line to the origin.

It should be noted, however, that lines delimiting a traffic lane are not perfectly straight lines. Generally, these are clothoids, that is, lines with continuous curvature. In order to optimally exploit the process according to the invention, it is intended to transpose the principle of Hough to the analysis of such clothoids.

Indeed, a vehicle in which the method according to the invention is implemented a priori evolves within a traffic lane, substantially parallel to the lines that delimit it. According to one embodiment, the detection of these lines can thus be approximated, in the Hough space, with a search for lines whose coefficients ‘a’ are close to 0, and the coefficients ‘b’ are inferior to the maximum distance to which it is desired to detect lines of separation of the traffic lanes, on either side of the vehicle.

This filtering makes it possible to limit the cases of false positives. In the case of a generalized Hough transform, applied to clothoids, the principle and the objective of the filtering remain indeed identical.

In addition, the markings on the ground materializing the separation lines of the traffic lanes are always clearer than the road surface. Therefore, another filtering consists in considering only the gradients corresponding to clear lines on darker background, and of minimum size. This alternative simple filtering also allows to limit the cases of false positives.

According to one embodiment, it is also provided a temporal filtering of the line detection algorithm. With reference to FIG. 2, the aerial view 11, reconstructed from captured images 10 integrated over time, becomes the aerial view 12 after temporal filtering, allowing a better identification of the lines of separation 21, 22 between the traffic lanes.

It should be noted that any other algorithm for detecting lines on the reconstructed aerial view can also be implemented, particularly in the context of the method according to the invention.

When several lines materialized by a marking on the ground are detected, the detection of the traffic lane in which the vehicle evolves is solely performed through the identification of the relevant lines, corresponding to the lines closest to the left and to the right of the said vehicle and the lateral position of the vehicle in its traffic lane is easily determinable.

According to an embodiment shown in FIG. 2, the method provides, for example, for choosing the center of the vehicle as the origin 0, the lateral position of the vehicle 100 in the lane being calculated according to the width of the vehicle, so that −1 corresponds to the presence of the left wheels on the left line, and 1 to the presence of the right wheels on the line on the right. Thus, the values between −1 and 1, for example 0.55 as in FIG. 2, correspond to a vehicle within its traffic lane, while the values beyond −1 and 1 indicate a vehicle straddling two lanes of traffic.

It should be noted that any other algorithm allowing to estimate the relative lateral position of the vehicle with respect to the separation lines of the traffic lanes, detected in the aerial view reconstructed in accordance with the steps described above, can also be implemented in the context of the method according to the invention.

Therefore, the method according to the invention comprises a step 4 of determining an estimated level of attention of the driver at an instant t3=t−dt3, dt3 being positive, the instant t3 being posterior to the instant t2 and the instant t3 being posterior or equal to the instant t1, depending:

-   -   on the evolution of the lateral position of the vehicle in the         aerial view between the instants t2 and t3,     -   on the profile analysis of a segment of a road belonging to the         reconstructed aerial view at the current instant t and         corresponding to a sequence of images captured between the         instant t1 and the current instant t, said segment being at         least partially located in front of the vehicle at the instant         t3.

Indeed, the analysis of the level of attention of the driver is carried out at an instant t3 set in the past relative to the current instant t. Thus, if the instant t3 and the instant t1 are equal, then the portion of the road segment appearing on the aerial view and corresponding to the images captured between the instant t1 and the current instant t is entirely located upstream of the vehicle, at the instant “set in the past” t3=t1. If the instant t3 is posterior to the instant t1, then the portion of the road segment appearing on the aerial view and corresponding to the images captured between the instant t1 and the current instant t is partially located upstream of the vehicle and partially located at the rear of the vehicle, at the instant “set in the past” t3 posterior to t1.

According to step 4 of the method according to the invention, at the instant t3 when the driver's attention level is determined, in the time marker of the vehicle, the reconstructed aerial view consequently always comprises a portion of the road segment located upstream of said vehicle. The profile of this segment located upstream of the vehicle is analyzed to establish an estimate of the level of attention of the driver, also depending on the evolution over time of the lateral position of the vehicle.

In addition, according to the invention, the successive aerial views of road segments are stored, as well as the successive estimated lateral positions of the vehicle, the storage being provided as long as necessary so that it is possible to know all the successive positions of the vehicle between the moment when it entered the reconstructed segment and the current instant t.

It should be noted that, for the application considered, the time shift and the delay induced by the fact that the driver's attention level is determined at an instant t3 set in the past relative to the current instant t are perfectly acceptable.

Furthermore, it is specified that, in the particular case of a traffic jam or slow speed, the number of successive lateral positions of the vehicle can be very high to cover the entire segment. For this reason, according to one embodiment, not all positions are necessarily stored in this case; only those sufficiently distant from each other are stored.

Thus, according to the invention, the analysis of the evolution of the lateral position of the vehicle on the segment allows to directly perform an assessment of the level of attention of the driver.

According to a preferred embodiment, the method further comprises capturing images of the driver's face whose analysis, by image processing according to known algorithms, gives an additional indication of the level of attention of the driver.

Thus, the analysis of the facial images is combined with the analysis of the evolution of the lateral position of the vehicle to determine the level of attention of the driver.

Furthermore, in order to implement this method, the invention also provides a system comprising a camera, a calculation unit and a storage unit, all suitably adapted. As described above, said camera may, for example, be a frontal camera or a parking aid camera of the type used in existing vehicles.

It is specified that the present invention is not limited to the examples described above and is capable of numerous variants accessible to those skilled in the art. 

1. Method for assessing the level of attention of the driver of a moving vehicle in a traffic lane, comprising the following steps: continuously capturing images (10) of the ground, at the front and/or rear of the vehicle (100), by means of at least one adapted camera, said images (10) corresponding to a surface on the ground having a width at least equal to a width of a traffic lane and a depth, reconstructing an aerial view (11, 12) of a road segment at successive current instants t by integration over time of the captured images (10) between an instant t1=t−dt1 and the current instant t, dt1 being positive, estimating the lateral position of the vehicle (100) in the reconstructed aerial view (11, 12) at said successive current instants t, and storing said estimated positions of the vehicle between an instant t2=t−dt2 and the current instant t, dt2 being positive and independent of dt1, determining an assessed level of attention of the driver at an instant t3=t−dt3, dt3 being positive, the instant t3 being posterior to the instant t2 and the instant t3 being posterior or equal to the instant t1, according to: the evolution of the lateral position of the vehicle in the aerial view between the instants t2 and t3, the analysis of the profile of a portion of road belonging to the aerial view reconstructed at the current instant t and corresponding to a sequence of captured images between the instant t1 and the current instant t, said portion of road being at least partially located upstream of the vehicle at the instant t3.
 2. The method according to claim 1, comprising, after the step of reconstructing an aerial view (11, 12) of the ground, detecting at least one line forming a ground marking delimitation of a traffic lane in said reconstructed aerial view, estimating the position of the vehicle (100) in the reconstructed aerial view (11, 12) consisting in determining the relative position of said vehicle with respect to said at least one line (21, 22).
 3. The method according to one of the preceding claims, further comprising: capturing images of the driver's face, analyzing the images of the driver's face, the determination of the assessed level of attention of the driver being also a function of said analysis of the images of the driver's face.
 4. The method according to one of the preceding claims, wherein the estimation of the relative position of the vehicle (100) with respect to said at least one line (11, 12) in the reconstructed aerial view comprises the assembly of successive captured images (10) corresponding to a ground surface having a depth determined according to the speed of the vehicle (100).
 5. The method according to claim 1, wherein detecting at least one line (21, 22) forming a ground marker delimiting a traffic lane in the reconstructed aerial view (11, 12) comprises the implementation of a Hough transform.
 6. The method according to one of the preceding claims, further comprising a driver warning step when the vehicle (100) crosses the said at least one line.
 7. The method according to one of the preceding claims, said lane width being equal to five meters.
 8. The method according to one of the preceding claims, said depth of the ground surface of the captured images being less than two meters.
 9. Device for assessing the level of attention of the driver of a vehicle in a traffic lane, comprising at least one camera for continuously capturing images (10) of the ground, at the front and/or at the rear of the vehicle, a calculation unit and a storage unit, configured to implement the method according to one of the preceding claims.
 10. The device according to the preceding claim, wherein said at least one camera is a frontal camera disposed at the front of the vehicle. 